1. Field of the Invention
The present invention relates to a layered ceramic electronic component element housing package for mounting and housing semiconductor elements, liquid crystal oscillators, and other electronic component elements, and more specifically, to a smaller and lower-profile electronic component element housing package capable of reducing the size and thickness of the ceramic substrate in order to house electronic component elements in a package and reduce the thickness and size of the device on which the elements are mounted.
2. Background Art
Conventionally, a plurality of ceramic green sheets was used in layered ceramic electronic component element housing packages. The ceramic green sheets were made by adding a sintering agent such as silica (SiO2), magnesia (MgO), or calcia (CaO) at the rate of 6-9% by weight to 91-94% by weight of alumina (Al2O3), mixing in an organic binder, a plasticizer, and a solvent or the like to make a slurry, which is then formed into a sheet shape by the doctor blade method. On the respective ceramic green sheets, metalized printed wiring for electrical conduction use having a via conductor and a through hole conductor for forming an electrically conductive state between layers above and below is formed by screen printing using a conductive paste made by mixing high-melting point metals such as tungsten (W) and molybdenum (Mo) with a solvent or the like. In addition, the plurality of ceramic green sheets on which the metalized printed wiring is formed is layered by aligning and applying heat and pressure, then simultaneously firing the ceramic green sheets with high-melting point metal at a temperature of 1550-1600° C. in a reducing atmosphere to form a layered ceramic electronic component element housing package having a ceramic substrate surface, an interior, and inter-layer metalized layers. This electronic component element housing package is configured so that the sintering temperature of the sheets is lowered by adding the sintering agent to the sheets, thus making it possible to perform sintering without any difficulty for sintering with the tungsten and molybdenum. In addition, the electronic component element housing package is configured so that the ceramic constituent material in the ceramic substrate other than the 91-94% by weight of alumina powder is a sintering agent such as silica (SiO2), calcia (CaO), or magnesia (MgO), and is configured so that the bond strength of the metalized layers of tungsten and molybdenum formed on the ceramic substrate can be increased by the glass component of the sintering agent.
However, electronic component element housing package of mainly alumina as described above contains a comparatively large amount of sintering agent at 6-9% by weight. While the firing temperature can be lowered, the bending strength of the ceramic substrate itself drops to around 320 MPa. Thus, there is a limit to which the thickness of the ceramic substrate can be reduced. Consequently, if the thickness of the ceramic substrate is reduced, the electronic component element housing package becomes unable to withstand thermal stress during metal cover bonding after electronic component mounting. In addition, if the thickness is increased, after the electronic components are mounted this electronic component element housing package becomes unable to be used as a small, low-profile package capable of being mounted on module capable of supporting thinner and smaller sizes.
A disclosure has been made of an invention in which a sintered body is formed containing 2.0-27.0% by weight of zirconium oxide on at least one of the ceramic substrate or the cover in order to increase the bend strength of ceramic substrates in conventional electronic component element housing packages (for example, see Patent Document 1). According to this invention, a container having a ceramic substrate and a cover seals semiconductor elements airtight inside the container, and after a semiconductor device is rendered, the airtight seal can be maintained completely even if outside force is applied to the ceramic substrate or the cover.
In addition, an invention has been disclosed in which a ceramic substrate having improved bending strength for use as a semiconductor device is made from a sintered body with alumina as the main constituent element and zirconia added. The material composition of the ceramic substrate is selected from within a range of 70-90% by weight for alumina and 10-30% by weight for the zirconia additive (for example, see Patent Document 2). According to this invention, the ceramic substrate has a higher bending strength and pliability (toughness) than those made of alumina, thus making a thinner ceramic substrate possible.